Anton von Leeuwenhoek didn't exactly know what he'd see when he took a gander at his own semen sample in a homemade microscope. It was 1677, and science had yet to figure out the ingredients of ejaculate, not to mention that von Leeuwenhoek got into microscopes on a lark as a hobby from his day job as a draper, or cloth salesman [source: RadioLab]. Peering into his newfangled microscope that magnified the fluid 300 times, von Leeuwenhoek spied "a multitude of live animalcules more than a million, having the size of a grain of sand," as he wrote to London's Royal Society in November 1677 [source: Karamanou].
Although with this observation, human spermatozoa had been revealed for the first time in history, it would still take a while to get the record straight about how sperm contribute to the baby-making process. Von Leeuwenhoek's contemporaries, in fact, imagined each sperm contained a tiny person, wishing and hoping to be delivered safely to a female womb [source: RadioLab].